Hard metal composition and method of making the same



Feb. 2, 1932. HOYT 1,843,768

HARD METAL COMPOSITION AND METHOD OF MAKING THE SAME Filed April 6. 1927 Inv eniron: Examuel L .Hoyt,

HLs Attorney.

atented Feb. 2, 1932 SA'MIU'EI. L. HOYT, OF .SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF'NEW YORK HARD METAL COMPOSITION AND METHOD OF MAKING THE SAME Application filed April 6,

V ture in a mold under pressure and then heating the pressed bar to its sintering temperature. Metallic compositions formed in this manner and containing from about 5 to of auxiliary metal provide a finished product which is suitable for use as dies or cutting tools depending upon the amount of auxiliary metal employed. Such a product, however, contains voids and is always more or less porous. The product as made by the process to be presently described differs from the former process by being essentially free from such voids. It is not to.be understood that the former product is porous to the extent that it will absorb a fluid, for that would mean that the cavities are interconnecting.

Butit is to be understood that these voids lower the hardness of .the product (as will be described) and that they make it difficult to get an extremely smooth, polished surface.

In the former process it has been considered inadvisable to employ a content of auxiliary metal greater than 20 per cent,-

since above this point the metal cutting tools obtained by the process have no particular. advantage over ordinary high speed cutting and which is suitable for use as a metal cut-* 1927. Serial No. 181,536.

ting tool, a wire drawing die, or as a bearing material. V

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best' be understood from reference to the following specification when considered in connection with the accompanying drawing in which the single figure shows diagrammatically a per spective view partly in section and partly in elevation of a mold and associated electrodes whereby my invention may be carried into effect. i

In carrying out my invention a metal, preferably of the sixth group of Mendelejeifs periodic table, such as tungsten in pow= dered form, may be first formed into tungsten carbide by heating the tungsten at an elevated temperature either in the presence of finely divided carbon, such as sugar carbon, or in the presence of a gas containing carbon, such as methane or ordinary illuminating gas. The carbide thus formed may contain from 3 to 10 per cent of carbon and preferably from 5.5 to 6.2 per cent carbon. The carbide is powdered and thoroughly mixed with about 5 per cent or more of a powdered auxiliary metal of the iron group, as cobalt, the amount of auxiliary inetal employed depending upon the use to which the finished product'is to be put. The powdered mixture is placed in a hollow carbon or othersuitable mold 1, having an opening 2 extending therethrough, and between the oppositely disposed electrodes 3 and 4 both of which are movable in the opening in the mold. A pressure of about 1000 pounds per square inch is applied through the electrodes to the confined powdered mixture 5 and a current is simultaneously supplied'through' the electrodes by means of the connectors 7 and- 8, thereby heating the powdered material to a temperature sufficiently high to sinter the mass thoroughly and tocause the auxiliary metal to become uniformly distributed through theentiremass. I have found it advisable to employ a temperature varying from 1300 C. to 1450 C., although the temperature will vary somewhat with 'difi'erent ing point of the auxiliary metal but is the sintering temperature of the mixture, i. e., the temperature at which the particles of the campact mass. This temperature should be maintained for a period of time varying from about one to several minutes in order to obtain the best results. lVhen pressure is applied to the powdered materials at this temperature the auxiliary metal flows through the entire mass substantial-1y filling all the voids between the particles of car hide and cementing the carbide particles into a very hard, dense and uniform mass. The fracture of the finished material is very fine and dense even when examined under the microscope and indicates that the porosity which usually exists in metal compositions of this character has been to a very large degree eliminated.

Metal cutting tools made by my process and from a composition containing about 13 per cent by weight of auxiliary metal, as oobalt, about 6% carbon, and the remainder tungsten have shown a hardness number of about 89 on the Rockwell scale employing no load. This maybe compared with hardened steel which runs 84 to 85 as a maximum, tool steel which runs to 81 as a maximum, and with a sintered metal composition consistin of tungsten carbide and cobalt not presse at the sintering temperature of the mixture which runs 85 as a maximum. From the above figures it will be seen that a powdered composition of tungsten carbide and cobalt pressed at the sintering temperature of the mixture gives a hardness number about four points greater than that obtained by the same composition which is merely sintered. The tungsten carbide employed in the above com positions was made from sugar carbon. A higher degree of hardness will be obtained if gas carbon is substituted for sugar carbon in the mixture.

Metal cutting tools made from a powdered mixture of tungsten carbide and cobalt pressed at the sintering temperature of the mixture have generally the smooth bright appearance of high grade tool steel and do nothave the usual mattappearance of composite metals. The material formed in this manner-is capable of taking a very keen sharp edge similar to the edge which can be put on any good metal cutting tool. Such tools will maintain their cutting edge for unusually long periods of time even when subjected to unusually heavy loads. As an example, it may be stated that tools consisting of a composition of tungsten carbide and 20 per 7 cent cobalt and formed by sintering under pressure will take a light finishing cut on cast iron at a surface speed of about 300 feet per minute, and that they will cut machine swaged molybdenum rods one inch in diameter at a speed which is approximately the same as that which would be employed for cutting brass. By way of contrast, it may be stated, that the best high grade tool steel would not start a light finishing cut on cast iron at 300 feet per minute, nor would it start a cut on the swaged molybdenum rod. In the latter case, the molybdenum rod merely ground away the high speed tool.

Although the above method has been described mainly in connection with tungsten carbide and cobalt, the same method may be applied to other powdered or finely divided mixtures if desired. For example, powdered tungsten and copper may be formed into a compact, hard mass, suitable for use as welding electrodes, by pressing the mixed tungsten and copper at the sintering temperature of the mixture.

Although various hard metals may be combined with elements of the iron group to form refractory metal compositions, I have found that for metal cutting tools the best results may be obtained by a composition comprising tungsten, carbon and cobalt.

What]: claim as new and desire to secure by Letters Patent of the United States, is,-

1. The method of forming a metallic structure containing tungsten, carbon and cobalt, which comprises mixing materials comprising the structure in powdered form, heating the mixture to its sintering temperature and simultaneously applying pressure thereto.

2. A sintered metal composition consisting largely of tungsten and containing an appreciable amount of carbon and an auxiliary metal of the iron group, said composition being substantially free from voids.

3. A sintered metal composition consisting largely of tungsten but containing appreciable amounts of carbon and cobalt, said composition being substantially free from voids.

4. A sintered metal composition consisting largely of tungsten carbide but containing about 13% of cobalt, said composition being substantially free from voids.

5. The method of forming a metallic structure consisting of finely divided tungsten carbide and a finely divided element of the iron group, which comprises mixing said carbide and element, heating the mixture to its sintering temperature, and simultaneously applying pressure thereto. l.

6. The method of forming a metallic composition consisting largely of tungsten-carbide but containing appreciable amounts of cobalt which comprises pressing powdered materials comprising the composition while simultaneously heating the composition to its sintering temperature.

7. The method of forming a metallic composition consisting largely of tungsten-carbide but containing appreciable amounts but not more than 25% of cobalt, which comprises pressing powdered materials comprising the composition while simultaneously heating the composition to its sintering temperature for a few minutes only.

8. The method of forming a metallic composition consisting largely of tungsten-carbide but containing an appreciable amount of metal of the iron group, which comprises pressing powdered materials comprising the composition While simultaneously heating the composition to its sintering temperature.

9. The method of forming a metallic composition consisting largely of tungsten-carbide but containing an a preciable amount but not more than 25% 0? metal of the iron group, which comprises pressing powdered materials comprising the composition while simultaneously heating the composition to its sintering temperature for a few minutes only.

In witness whereof, I have hereunto set my hand this 5th day of April, 1927.

SAMUEL L. HOYT. 

